Redundant ethernet automatic protection switching access to virtual private lan services

ABSTRACT

Embodiments disclosed herein provide redundant connectivity between an Ethernet Automatic Protection Switching (EAPS) access network and a Virtual Private LAN Service (VPLS) network. A first VPLS node is provided to function as an EAPS controller node. A second VPLS node is provided to function as an EAPS partner node. The first and second VPLS nodes are linked by a pseudowire and an EAPS shared-link. Additional EAPS nodes are also provided. The additional EAPS nodes are linked to each other and one of the additional EAPS nodes is designated as a master node. Links are also established between the VPLS nodes and the EAPS nodes such that one or more EAPS rings are formed. Each EAPS ring includes the shared-link between the first and second VPLS nodes. The EAPS rings are monitored to detect link failures. When a failure of the pseudowire shared-link between the first and second VPLS nodes is detected, all pseudowire links associated with the first VPLS node are disabled if any of the EAPS nodes has a path to both of the VPLS nodes. Otherwise, the existing pseudowire links associated with the first VPLS node are maintained.

CLAIM OF PRIORITY

The present patent application is a continuation of and claims thebenefit of the earlier filing date of non-provisional U.S. patentapplication Ser. No. 13/165,534, filed on Jun. 21, 2011, entitled“REDUNDANT ETHERNET AUTOMATIC PROTECTION SWITCHING ACCESS TO VIRTUALPRIVATE LAN SERVICES,” which is a continuation of and claims the benefitof the earlier filing date of non-provisional U.S. patent applicationSer. No. 12/101,603, filed on Apr. 11, 2008, entitled “REDUNDANTETHERNET AUTOMATIC PROTECTION SWITCHING ACCESS TO VIRTUAL PRIVATE LANSERVICES.”

FIELD

Embodiments of the invention relate to computer networking, and moreparticularly to redundantly connecting a VPLS network with an EAPSnetwork.

BACKGROUND

Computer networks are becoming increasingly important for businesses andcommunities. Cost efficiency, network capacity, scalability andflexibility are all important considerations in building and maintainingvarious networks. With a wide variety of services, protocols andtechnologies, it can be difficult to integrate and/or provideconnectivity between different types of networks.

Virtual Private LAN Service (VPLS) is a way to provide Ethernet basedmultipoint to multipoint communication over IP/MPLS networks. VPLSallows geographically dispersed sites to share an Ethernet broadcastdomain by connecting sites through pseudowires (PWs).

Ethernet Automatic Protection Switching (EAPS), offered by ExtremeNetworks of Santa Clara, Calif., is a solution for fault-tolerantnetworks. EAPS provides for a loop-free operation and a sub-second ringrecovery. EAPS version 2 (EAPSv2) is configured and enabled to avoid thepotential of super loops in environments where multiple EAPS domainsshare a common link. EAPSv2 functions use the concept of a “controller”and a “partner” mechanism. Shared port status is verified using healthprotocol data units (PDUs) exchanged by controller and partner. When ashared-link goes down, the configured controller will open only onesegment port for each of the protected VLANs, keeping all other segmentports in a blocking state.

The Internet Engineering Task Force (IETF) RFC 4762, entitled “VirtualPrivate LAN Service (VPLS) Using Label Distribution Protocol (LDP)Signaling” proposes the use of redundant pseudowires (PWs) to attach toa VPLS core network. However, this technique is applicable only where asingle attachment node is necessary. The IETF draft entitled “VPLSInteroperability with CE Bridges” also discusses redundant access toVPLS core networks. However, this technique does not address ring-basedaccess networks and it utilizes only a single active attachment to aVPLS network. Likewise, the IETF draft entitled “Pseudowire (PW)Redundancy” discusses redundant access to VPLS core networks, but failsto address ring-based access networks and only utilizes a single activeattachment to a VPLS core network.

SUMMARY OF THE INVENTION

Embodiments disclosed herein provide redundant connectivity between anEthernet Automatic Protection Switching (EAPS) access network and aVirtual Private LAN Service (VPLS) network. A first VPLS node isprovided to function as an EAPS controller node. A second VPLS node isprovided to function as an EAPS partner node. The first and second VPLSnodes are linked by a pseudowire. This pseudowire is normallytransmitted across an EAPS shared-link. Additional EAPS nodes are alsoprovided. The additional EAPS nodes are linked to each other and one ofthe additional EAPS nodes is designated as a master node. Links are alsoestablished between the VPLS nodes and the EAPS nodes such that one ormore EAPS rings are formed. Each EAPS ring includes the shared-linkbetween the first and second VPLS nodes. The EAPS rings are monitored todetect link failures. When a failure of the shared-link between thefirst and second VPLS nodes is detected, all pseudowire links associatedwith the first VPLS node are disabled if any of the EAPS nodes has apath to both of the VPLS nodes. Otherwise, the existing pseudowire linksassociated with the first VPLS node are maintained.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description includes discussion of figures havingillustrations given by way of example of implementations of embodimentsof the invention. The drawings should be understood by way of example,and not by way of limitation. As used herein, references to one or more“embodiments” are to be understood as describing a particular feature,structure, or characteristic included in at least one implementation ofthe invention. Thus, phrases such as “in one embodiment” or “in analternate embodiment” appearing herein describe various embodiments andimplementations of the invention, and do not necessarily all refer tothe same embodiment. However, they are also not necessarily mutuallyexclusive.

FIG. 1 is a block diagram illustrating a VPLS-EAPS configurationaccording to various embodiments.

FIG. 2 is a block diagram illustrating a VPLS-EAPS configurationaccording to various embodiments.

FIG. 3 is a block diagram illustrating a VPLS-EAPS configurationaccording to various embodiments.

FIG. 4 is a block diagram illustrating a VPLS-EAPS configurationaccording to various embodiments.

FIG. 5 is a block diagram illustrating a VPLS-EAPS configurationaccording to various embodiments.

FIG. 6 is a flow diagram illustrating a process for redundantconnectivity between a VPLS network and an EAPS network according tovarious embodiments.

FIG. 7 is a block diagram illustrating a suitable computing environmentfor practicing various embodiments described herein.

FIG. 8 is a block diagram illustrating a routing device according tovarious embodiments.

DETAILED DESCRIPTION

As provided herein, methods, apparatuses, and systems enable redundantconnectivity between a Virtual Private LAN Service (VPLS) network and anEthernet Automatic Protection Switching (EAPS) network. Moreparticularly, multiple active attachments to a VPLS network are providedin various embodiments.

FIG. 1 is a block diagram illustrating a VPLS-EAPS configurationaccording to various embodiments. As used herein, a VPLS-EAPSconfiguration involves multiple attachment points between a VPLS networkand an EAPS network, the attachments normally active. As shown, VPLScore nodes 110, 112, 114 and 116 are linked via pseudowires. As usedherein, a link refers to any line or channel over which data istransmitted. A pseudowire, as used herein, refers to a mechanism foremulating various networking or telecommunications services acrosspacket-switched networks, such as those mechanisms that use Ethernet,Internet Protocol (IP), Label Switched Paths (LSPs), Multi-protocolLabel Switching (MPLS) and/or the like. Emulated services can include T1leased line, frame relay, Ethernet, Asynchronous Transfer Mode (ATM),time-division multiplexing (TDM), or Synchronous Optical Networking(SONET)/Synchronous Digital Hierarchy (SDH). As discussed in RFC 3985entitled “Pseudo Wire Emulation Edge-to-Edge [PWE3] Architecture,” apseudowire delivers only the functionality necessary to emulate a wirewith some required degree of fidelity for some specific servicedefinition.

As shown in FIG. 1, VPLS core nodes 110 and 112 are attached to the EAPSaccess ring. Rather than having core node 110 or 112 function as theEAPS master node, distribution node 124 is designated as the masternode. When a network failure is detected on the ring, the master node inan EAPS system receives control messages over the control VLAN, thecontrol messages indicating the network failure. During normaloperation, the master node blocks the protected data VLAN traffic fromtraversing its secondary port. During a network failure, the master nodeunblocks its secondary port and routes the protected data VLAN trafficthrough its secondary port. The secondary port is re-blocked once thefailure has been fixed. In various embodiments, any node in the EAPSring that is not a VPLS node can be designated as the EAPS master node.In various embodiments, the VPLS core nodes attached to the EAPS ringfunction as EAPS controller and partner nodes, respectively. In FIG. 1,core node 110 functions as the controller node while core node 112functions as the partner node. The EAPS controller node (e.g., core node110) includes a controller state machine, which keeps track of whetherEAPS nodes on the ring have access to both attached VPLS nodes (e.g.,core nodes 110 and 112).

In various embodiments, when a VPLS customer VLAN (or VMAN) is attachedto an EAPS ring, as shown in FIG. 1, the EAPS ring segment between corenodes 110 and 112 is removed in favor of a pseudowire connection betweencore nodes 110 and 112. The term “shared-link,” as used herein, refersto a special EAPS link that is typically shared among multiple EAPSrings. While a shared-link is often shared among multiple EAPS rings, ashared-link can also be maintained for a single EAPS ring. In additionto facilitating port management among multiple EAPS rings, functionsand/or mechanisms associated with the shared-link (e.g., controller nodestate machine, etc.) may be used to assist in managing communicationbetween EAPS and VPLS. The EAPS master node (e.g., node 124) does notnecessarily have or receive any information regarding the connectionchange between core nodes 110 and 112. However, the EAPS functionalityon core nodes 110 and 112 do have information regarding the connectionchange given that the connection change requires configuring anEAPS-protected VLAN with only one port on the ring. It should be notedthat this configuration does not change the EAPS control VLAN—the EAPSring is still complete and the EAPS master node (e.g., node 124) stillblocks a port on the customer access VLAN when the ring is intact.

FIG. 2 shows an example of a link failure, in this case between nodes122 and 124. From a connectivity perspective, various embodiments of theVPLS-EAPS configuration appropriately handle access ring failures likethe link failure shown in FIG. 2. When the EAPS master node (e.g., node124) detects a topology change (e.g., due to a link failure notificationfrom a node on the ring, a hello timeout, etc.), the master nodeunblocks its secondary port on the protected VLAN. The only differencein FIG. 2 (as compared to FIG. 1) is that the link failure andsubsequent unblocking of the master node's secondary port causes node124 to now connect to the VPLS network via core node 112 instead of viacore node 110. Thus, connectivity is recovered.

The connectivity recovery scenario changes when the shared-link betweencore nodes 110 and 112 fails. As illustrated in FIG. 3, when theshared-link fails, the EAPS master node (e.g., node 124) again unblocksits secondary port (as it does whenever there is a failure on the accessring). However, when this occurs, both VPLS core nodes (i.e., nodes 110and 112) might receive a copy of any traffic that is not destined for anode on the EAPS access ring. For example, if the shared-link betweencore nodes 110 and 112 failed and distribution node 126 was trying tosend a packet to VPLS core node 116, core nodes 110 and 112 might eachreceive a copy of the packet. This would result in duplicate packetsbeing sent into the VPLS network. Additionally, given that thepseudowire between core nodes 110 and 112 could be reestablished using adifferent path (e.g., via the path from node 112 to node 116 to node 114to node 110), this scenario could result in a traffic loop on the EAPSaccess ring as well as a storm into the VPLS network. To prevent thisscenario from occurring, VPLS core node 110 (functioning as the EAPScontroller node) takes the action of removing and/or disabling allpseudowires associated with core node 110 when the shared-link betweencore nodes 110 and 112 fails. The removal of pseudowires can be seen inFIG. 3. Once the pseudowires have been removed and/or disabled, alltraffic traveling between the EAPS access network and the VPLS networkpasses through VPLS core node 112. When core node 110 (i.e., thecontroller node) detects that the shared-link between nodes 110 and 112is repaired, the pseudowires are reestablished.

When core node 110 removes its pseudowires, core node 110 also signalsits VPLS peers (e.g., VPLS core nodes 114, 116, and 112) to inform themthat the pseudowires are no longer active. In some embodiments, thissignaling is accomplished by completely withdrawing the pseudowires. Inother embodiments, the signaling is accomplished by indicating a“standby” state for the pseudowires.

FIG. 4 shows a link failure on both the shared-link (i.e., the linkbetween nodes 110 and 112) and on the access ring (e.g., between nodes122 and 124). In a dual failure scenario such as this, VPLS core nodes110 and 112 do not both receive a copy of ring traffic, unlike thescenario where only the shared-link fails. For example, in FIG. 4, theonly path to the VPLS network for distribution node 122 is through corenode 110 in this dual failure scenario. Similarly, the only path to theVPLS network for distribution node 128 is through core node 112.Accordingly, in a dual failure scenario where one of the failed links isthe VPLS core shared-link, core node 110 maintains its pseudowiresrather than removing and/or disabling the pseudowires.

FIG. 5 illustrates multiple parallel EAPS access rings attached to aVPLS core network. As shown, each of the EAPS rings is attached to bothcore node 210 and core node 212. Each of the EAPS rings shares the link(i.e., the shared-link) between node 210 and node 212. Functions and/ormechanisms associated with the shared-link manage and/or maintain EAPStopology information that can be propagated to the VPLS network. Here,as long as any of the parallel EAPS rings is complete, there exists apath to both core VPLS nodes—in this case, nodes 210 and 212. When theshared-link between nodes 210 and 212 is in a failed state (as shown),the EAPS master node on each ring unblocks its secondary port. For thetwo inner EAPS rings, illustrated in FIG. 5, this causes no problemsbecause each of these rings has an additional link failure on the ringwhich prevents nodes in these rings from having a path to both VPLS corenodes (i.e., nodes 210 and 212). However, the outer ring has no otherlink failures. Thus, distribution nodes (e.g., 250, 252, 254 and 256) onthis outer ring do have a path to both VPLS nodes 210 and 212. It shouldbe noted that both VPLS nodes still perform L2 switching on all of theaccess rings. Therefore, all of the nodes on all three rings have a pathto both VPLS nodes. As discussed above, a path from an EAPS ring to bothcore nodes on the VPLS network can cause an access ring loop and/or aVPLS storm. Thus, in embodiments having parallel EAPS rings attached tothe VPLS core, the controller node (e.g., core node 210) must disableall pseudowires associated with the controller node if and when any ofthe parallel EAPS rings are complete or “up” (e.g., no link failures)and the shared-link is failed. If all parallel EAPS rings are in afailed state or “down” (e.g., at least one failed link on each ring),then the controller node (e.g., node 210) maintains all its existingpseudowires regardless of the state of the shared-link. The followingtable shows the recovery actions to be taken on the controller node invarious embodiments:

TABLE 1 Core Link State Ring State Core Link Up Core Link Down AnyParallel Ring Up PWs Active PWs Inactive Any Parallel Ring Down PWsActive PWs Active

In various embodiments, changes in topology on either the access ring(s)or the VPLS network may cause changes to the path(s) used to reachcustomer devices. For example, in FIG. 2, the path that distributionnode 124 would take to reach other parts of the VPLS network changesfollowing the failure on the access ring of the link between nodes 122and 124. Prior to failure of that link, node 124 reached the VPLSnetwork via core node 110. Following the failure, node 124 accesses theVPLS network via core node 112.

When the EAPS master node (e.g., node 124 in FIG. 1, node 222 in FIG. 5,etc.) detects a topology change, it sends a “flush FDB” message to itsother transit nodes (i.e., the other nodes on the ring). In someembodiments, the flush message causes the ring's MAC addresses to berelearned on each node in the ring. Given that the flush message is anEAPS message that is propagated to the other nodes on the ring, theflush message is not inherently propagated over the VPLS network. Also,the attachments at the remote VPLS nodes may not be utilizing EAPS.Using the above example, VPLS node 114 (FIG. 2) would expect to findnode 124 via the pseudowire between VPLS node 114 and VPLS node 110.However, upon the occurrence of a link failure between nodes 122 and124, any traffic sent from VPLS node 114 to node 124 via VPLS node 110will not reach its destination given that VPLS node 114 is not aware ofthe topology change and is configured to send traffic on a path throughthe failed link. To overcome this problem, EAPS informs VPLS about anyreceived EAPS “flush FDB” messages on both the controller and partnernodes (e.g., nodes 110 and 112). The controller and partner nodes canthen propagate this information so that other VPLS nodes can flush theirrespective forwarding databases (e.g., MAC addresses, etc.). Given thatMAC addresses, for example, are learned from a particular originatingnode (e.g., VPLS node 116 learns the MAC address for node 128 from VPLSnode 112), both the controller and the partner node inform the otherVPLS nodes of any topology changes.

FIG. 6 is a flow diagram illustrating a process for redundantconnectivity between a VPLS network and an EAPS network. Two VPLS nodesare provided 310 to function as an EAPS controller node and partnernode, respectively. The two VPLS nodes are linked by a pseudowire acrossan EAPS shared-link. Additional EAPS nodes are also provided 320. Theadditional EAPS nodes are linked to each other and one of the additionalEAPS nodes is designated as a master node. Links are also establishedbetween the VPLS nodes and the EAPS nodes such that one or more EAPSrings are formed 330. Each EAPS ring includes the shared-link betweenthe first and second VPLS nodes. The EAPS rings are monitored 340 todetect link failures. When a failure of the pseudowire shared-linkbetween the first and second VPLS nodes is detected 350, it isdetermined 360 whether any of the EAPS nodes has a path to both of theVPLS nodes. If yes, then all pseudowires associated with the controllernode are disabled 370. If no, then the existing pseudowire linksassociated with the first VPLS node are maintained 380.

FIG. 7 is a block diagram illustrating a suitable computing environmentfor practicing various embodiments described herein. Collectively, thesecomponents are intended to represent a broad category of hardwaresystems, including but not limited to general purpose computer systemsand specialized network switches.

Computer system 700 includes processor 710, I/O devices 740, main memory720 and flash memory 730 coupled to each other via a bus 780. Mainmemory 720, which can include one or more of system memory (RAM), andnonvolatile storage devices (e.g., magnetic or optical disks), storesinstructions and data for use by processor 710. Additionally, thenetwork interfaces 770, data storage 760, and switch fabric 750 arecoupled to each other via a bus 780. Data storage 760 represents therouting database (e.g., forwarding database tables, etc.) describedherein as well as other storage areas such as packet buffers, etc., usedby the switch fabric 750 for forwarding network packets or messages.

The various components of computer system 700 may be rearranged invarious embodiments, and some embodiments may not require nor includeall of the above components. Furthermore, additional components may beincluded in system 700, such as additional processors (e.g., a digitalsignal processor), storage devices, memories, network/communicationinterfaces, etc.

In the illustrated embodiment of FIG. 7, methods and apparatuses forproviding redundant connectivity between an EAPS network and a VPLSnetwork according to the present invention as discussed above may beimplemented as a series of software routines run by computer system 700of FIG. 7. These software routines comprise a plurality or series ofinstructions to be executed by a processing system in a hardware system,such as processor 710. Initially, the series of instructions are storedon a data storage device 760 (e.g., in a route manager database), memory720 or flash 730.

FIG. 8 illustrates the various components of a routing device that maybe used in various embodiments. Routing device 810 includes a VPLScontrol component 812, a pseudowire (PW) control component 814, an EAPScontrol component 816, and a Bridge control component 818. The VPLScontrol component 812 facilitates establishing a complete VPLS comprisedof multiple PWs. The PW control function 814 establishes the individualPWs and signals PW state information to peers. The EAPS control function816 monitors and controls

EAPS operation. The bridge control function 818 monitors and controlsnormal L2 bridge operation. The EAPS control function 816 provides theVPLS control 812 and/or PW control 814 functions with information aboutthe state of the EAPS shared-link and the EAPS ring connectivity. TheVPLS forwarding logic component 820, the PW forwarding logic component822, and the bridge forwarding component 824 combine to forward datapackets between PWs and VPLS customers. These forwarding components arecoupled via bus 826. Based on the logic of these components, traffic isrouted on the routing device ports 828. Routing device 810 is an exampleof a routing device that could be used for VPLS core nodes 110 and/or112 of FIG. 2, for example.

Various components described herein may be a means for performing thefunctions described herein. Each component described herein includessoftware, hardware, or a combination of these. The components can beimplemented as software modules, hardware modules, special-purposehardware (e.g., application specific hardware, application specificintegrated circuits (ASICs), digital signal processors (DSPs), etc.),embedded controllers, hardwired circuitry, etc. Software content (e.g.,data, instructions, configuration) may be provided via an article ofmanufacture including a computer readable medium, which provides contentthat represents instructions that can be executed. The content mayresult in a computer performing various functions/operations describedherein. A computer readable medium includes any mechanism that provides(i.e., stores and/or transmits) information in a form accessible by acomputing device (e.g., computer, PDA, electronic system, etc.), such asrecordable/non-recordable media (e.g., read only memory (ROM), randomaccess memory (RAM), magnetic disk storage media, optical storage media,flash memory devices, etc.). The content may be directly executable(“object” or “executable” form), source code, or the like. A computerreadable medium may also include a storage or database from whichcontent can be downloaded. A computer readable medium may also include adevice or product having content stored thereon at a time of sale ordelivery. Thus, delivering a device with stored content, or offeringcontent for download over a communication medium may be understood asproviding an article of manufacture with such content described herein.

Besides what is described herein, various modifications may be made tothe disclosed embodiments and implementations of the invention withoutdeparting from their scope. Therefore, the illustrations and examplesherein should be construed in an illustrative, and not a restrictivesense. The scope of the invention should be measured solely by referenceto the claims that follow.

1. (canceled)
 2. A method for providing redundant network connectivity,the method comprising: forwarding traffic in a network, wherein thenetwork comprises a plurality of Ethernet Automatic Protection Switching(EAPS) nodes, an EAPS shared-link, a first Virtual Private LAN Service(VPLS) node, and a second VPLS node, wherein the plurality of EAPS nodesare included in an EAPS ring, wherein the EAPS shared-link connects thefirst VPLS node to the second VPLS node, and wherein both the first VPLSnode and the second VPLS node are connected to one or more pseudowirelinks; detecting a network failure of the EAPS shared-link in order todetermine whether each of the plurality of EAPS nodes has a path to thefirst VPLS node and the second VPLS node; and disabling, in response todetecting the network failure of the EAPS shared-link, all pseudowirelinks associated with the first VPLS node when any of the plurality ofEAPS nodes has a path to both the first VPLS node and the second VPLSnode.
 3. The method of claim 2, wherein the network further comprises aplurality of VPLS nodes linked to the first VPLS node, wherein themethod further comprises communicating an indication of the disabledpseudowire links to the plurality of VPLS nodes linked to the first VPLSnode.
 4. The method of claim 2, wherein the method further comprisesreestablishing the disabled pseudowire links when the first VPLS nodedetects that the EAPS shared-link is operational.
 5. The method of claim2, wherein the method further comprises maintaining, in response to thedetected network failures, the pseudowire links associated with thefirst VPLS node when the plurality of EAPS nodes each lack a path toboth the first VPLS node and the second VPLS node.
 6. The method ofclaim 2, wherein the EAPS shared-link is a pseudowire link.
 7. Themethod of claim 2, wherein the method further comprises computing, usinga state machine, whether each of the plurality of EAPS nodes has accessto the first VPLS node and the second VPLS node.
 8. The method of claim2, wherein the first VPLS node and the second VPLS node are connected toone or more EAPS rings, wherein the one or more of EAPS rings utilizethe EAPS shared-link.
 9. The method of claim 8, wherein the methodfurther comprises configuring the first VPLS node to disable allpseudowire links associated with the first VPLS node when the EAPSshared-link fails and any of the one or more EAPS rings include an EAPSnode with a path to the first VPLS node and the second VPLS node. 10.The method of claim 2, wherein the method further comprises configuringone of the plurality of EAPS nodes to function as an EAPS master node,wherein the EAPS master node is configured to receive a control messageindicating a network failure in the network.
 11. The method of claim 10,wherein the method further comprises: blocking a secondary port of theEAPS master node; and unblocking, in response to detecting the networkfailure, the secondary port of the EAPS master node.
 12. A first routingdevice comprising: one or more ports to connect the first routing deviceto a network, wherein the network comprises a second routing device, aplurality of Ethernet Automatic Protection Switching (EAPS) nodes, andan EAPS shared-link, wherein the plurality of EAPS nodes are included inan EAPS ring, and wherein the EAPS shared-link connects the firstrouting device to the second routing device; processing circuitryconfigured to: forward traffic on a Virtual Private LAN Service (VPLS)network, wherein the VPLS network includes a plurality of pseudowirelinks associated with the first routing device; detect a network failureof the EAPS shared-link in order to determine whether each of theplurality of EAPS nodes has access to the first routing device and thesecond routing device; and disable, in response to detecting the networkfailure of the EAPS shared-link, the pseudowire links associated withthe first routing device when any of the plurality of EAPS nodes has apath to both the first routing device and the second routing device. 13.The first routing device of claim 12, wherein the VPLS network furthercomprises a plurality of VPLS nodes linked to the first VPLS node,wherein the first routing device is further configured to communicate anindication of the disabled pseudowire links to the plurality of VPLSnodes linked to the first VPLS node.
 14. The first routing device ofclaim 12, wherein the first routing device is further configured toreestablish the disabled pseudowire links when the first VPLS nodedetects that the EAPS shared-link is operational.
 15. The first routingdevice of claim 12, wherein the first routing device is furtherconfigured to maintain, in response to the detected network failures,the pseudowire links associated with the first routing device when theplurality of EAPS nodes each lack a path to both the first routingdevice and the second routing device.
 16. The first routing device ofclaim 12, wherein the EAPS shared-link is a pseudowire link.
 17. Thefirst routing device of claim 12, wherein the system further comprises astate machine configured to compute whether each of the plurality ofEAPS nodes has access to the first routing device and the second routingdevice.
 18. The first routing device of claim 12, wherein the firstrouting device and the second routing device are connected to one ormore EAPS rings, wherein the one or more of EAPS rings utilize the EAPSshared-link.
 19. The first routing device of claim 18, wherein the firstrouting device is further configured to disable all pseudowire linksassociated with the first VPLS node when the EAPS shared-link fails andany of the one or more EAPS rings include an EAPS node with a path tothe first routing device and the second routing device.
 20. The firstrouting device of claim 12, wherein the system further comprises an EAPSnode configured to function as an EAPS master node, wherein the EAPSmaster node is configured to receive a control message indicating anetwork failure in the network.
 21. The first routing device of claim20, wherein the EAPS master node is further configured to: block asecondary port of the EAPS master node; and unblock, in response todetecting the network failure, the secondary port of the EAPS masternode.